The present application relates to power conversion methods, systems, and devices, and more particularly to nonresonant conversion architectures.
Note that the points discussed below may reflect the hindsight gained from the disclosed inventions, and are not necessarily admitted to be prior art.
A new kind of power converter was disclosed in U.S. Pat. No. 7,599,196 entitled “Universal power conversion methods,” which is incorporated by reference into the present application in its entirety. This patent describes a bidirectional (or multidirectional) power converter which pumps power into and out of a link inductor which is shunted by a capacitor.
The switch arrays at the ports are operated to achieve zero-voltage switching by totally isolating the link inductor+capacitor combination at times when its voltage is desired to be changed. (When the inductor+capacitor combination is isolated at such times, the inductor's current will change the voltage of the capacitor, as in a resonant circuit. This can even change the sign of the voltage, without loss of energy.) This architecture has subsequently been referred to as a “current-modulating” or “Power Packet Switching” architecture. Bidirectional power switches are used to provide a full bipolar (reversible) connection from each of multiple lines, at each port, to the rails connected to the link inductor and its capacitor. The basic operation of this architecture is shown, in the context of the three-phase to three-phase example of FIG. 1 of U.S. Pat. No. 7,599,196, in the sequence of drawings from FIG. 12a to FIG. 12j of U.S. Pat. No. 7,599,196.
The ports of this converter can be AC or DC, and will normally be bidirectional (at least for AC ports). Individual lines of each port are each connected to a “phase leg,” i.e. a pair of switches which permit that line to be connected to either of two “rails” (i.e. the two conductors which are connected to the two ends of the link inductor). It is important to note that these switches are bidirectional, so that there are four current flows possible in each phase leg: the line can source current to either rail, or can sink current from either rail.
Many different improvements and variations are shown in the basic patent. For example, variable-frequency drive is shown (for controlling a three-phase motor from a three-phase power line), DC and single-phase ports are shown (FIG. 21 of U.S. Pat. No. 7,599,196), as well as three- and four-port systems, applications to photovoltaic systems (FIG. 23 of U.S. Pat. No. 7,599,196), applications to Hybrid Electric vehicles (FIG. 24 of U.S. Pat. No. 7,599,196), applications to power conditioning (FIG. 29 of U.S. Pat. No. 7,599,196), half-bridge configurations (FIGS. 25 and 26 of U.S. Pat. No. 7,599,196), systems where a transformer is included (to segment the rails, and allow different operating voltages at different ports) (FIG. 22 of U.S. Pat. No. 7,599,196), and power combining (FIG. 28 of U.S. Pat. No. 7,599,196).
Improvements and modifications of this basic architecture have also been disclosed in U.S. Pat. Nos. 8,391,033, 8,295,069, 8,531,858, and 8,461,718, all of which are hereby incorporated by reference.
The term “converter” has sometimes been used to refer specifically to DC-to-DC converters, as distinct from DC-AC “inverters” and/or AC-AC frequency-changing “cycloconverters.” However, in the present application the word converter is used more generally, to refer to all of these types and more, and especially to converters using a current-modulating or power-packet-switching architecture.
Power conversion is one of the most important applications of power semiconductors, and plays an important role in many systems. Power conversion can be used to shift the voltage of a power supply to match the operating requirements of a particular load, or to permit use of a variable-voltage or variable current supply, or to compensate for the variation expected in an unreliable power source, or to permit a unit to be usable with a variety of power inputs, or to compensate for shift in “power factor” when an AC supply is connected to a reactive load. In many cases there are different terms for particular kinds of power conversion, e.g. a DC-to-AC converter is often referred to as an inverter, and some types of AC-to-AC converter are referred to as cycloconverters. Many kinds of motor drive can be thought of as a kind of power conversion: for example, a variable-frequency drive can be regarded as a species of power converter in which the frequency of an AC output is adjustable. In the present application the term “power conversion” will be used to refer generically to all of these types.
The present inventor has previously filed on a new class of power converter device operation and device, which provides a nearly universal power conversion architecture. In one version of this architecture, each input line is connected to the middle of one phase leg having two bidirectional switches, and the switches are operated so as to drive the terminals of a link reactance from one input or the other. A corresponding output switch array is used to transfer energy from the link reactance into two or more output terminals as desired, to construct the output waveform desired. Preferably the link reactance includes an inductor which is shunted by a capacitor. This provides a nearly universal hardware architecture, which is operated to implement a desired power-conversion function. This architecture is suitable for DC-AC, AC-AC, and AC-DC conversion. However, the present application teaches additional improvements, which are applicable to these as well as other topologies.
Many DC-DC, DC-AC, and AC-AC Buck-Boost converters are shown in the patent and academic literature. The classic Buck-Boost converter operates the inductor with continuous current, and the inductor can have an input and output winding to form a transfer for isolation and/or voltage/current translation, in which case it is referred to as a Flyback Converter. There are many examples of this basic converter, all of which are necessarily hard switched and therefore do not have the soft-switched attribute, which leads to reduced converter efficiency and higher costs.
In a chain of patent applications dating back to 2006, the present inventor has disclosed a revolutionary new power conversion architecture, known as the “UPC” (or “Universal Power Conversion”) architecture. Some of these applications include published US applications US2008/0013351 and US2008/0031019, now issued as U.S. Pat. Nos. 7,599,196 and 7,778,045, all of which are hereby incorporated by reference. The present application describes further improvements which are particularly advantageous in connection with UPC architectures, and can also be applicable to other architectures.
Motor drives usually provide motor speed control, direction control, start/stop control, torque regulation and protection to components of motors against flows or overloads.
Small residential, commercials, low voltage or low power industrial appliances ordinarily use single-phase motor drives. However, for heavy industrial applications such as compressors or conveyor drives, single-phase motor drives are sometimes not appropriate for efficient work.
Motor drives can use variable-frequency speed depending on the application needs of power converters. Usually, power converters designed for single-phase applications only support single-phase motor drives. Power converters designed for three-phase applications only support three-phase motor drives. There exist various methods to make single-phase or three-phase power converters capable of supporting three-phase or single-phase motor drives, respectively. For example, single-phase power converters can employ additional components, such as electrolytic capacitors, to enable support for three-phase motor drives. However, such additional components are typically expensive, and this type of solution tends to result in poor workload performance, e.g., limited speed range.
Three-phase motor drives are often better adapted to use in industrial appliances than single-phase motor drives. Three-phase motor drive can deliver high power induction, secure power transfer and is capable of producing a rotating magnetic field. However, three-phase converters that exclusively deal with three-phase motor drives, and power converters with additional components, are often neither accessible nor suitable for use, e.g., for some small business and residential applications.